Metered medication dose dispensers take many forms, but have in common that a predetermined dosage (i.e., amount) of medication is dispensed during a dosage dispensing operation. One common form of metered medication dose dispenser is known as an inhaler. Inhalers are commonly used for the treatment of asthma and other respiratory conditions.
An inhaler typically takes the form of an aerosol dispensing assembly having an aerosol container and an actuator housing for receiving that container. In the case of a pressurized inhaler, the container includes medication that is formulated with a suitable propellant that is filled into the container to define an aerosol canister. The container is typically equipped with a medication dispenser, fitted by means of a ferrule, such as a valve, in particular, a metered dose valve, comprising a valve stem movable between closed and discharge positions. Such a container with medication therein (i.e., an aerosol canister) and having a dispenser thereon, thus defines a medication vial. The medication vial is not refillable, and is disposed of once the medication therein has been dispensed. The medication vial is typically used in conjunction with an actuator housing (which may be reusable) that has a patient port (e.g., a mouthpiece or a port adapted for nasal use). The actuator housing typically comprises a support block that has a socket adapted to receive the valve stem of the valve on the container of the medication vial, and has an orifice in communication with the socket and the patient port. The canister and the support block are reciprocally movable relative to each other along an axis to allow the valve stem to move to its discharge position during the operation or firing of the assembly, thereby dispensing a dose of the medication from the vial. The actuator housing also typically includes an elongate portion extending opposite the support block and providing a chamber to house at least a portion of the container of the vial. There are many related design features of the actuator housing and the medication vial that are employed in order to achieve the desired medication dispensing performance (i.e., the dispensing of one metered amount or dose of sprayed medication of appropriate particle size distribution each time the aerosol dispensing assembly is actuated by a user).
To dispense a dose of medication, an inhaler user normally squeezes or pushes down on the inhaler in an axial direction causing a relative movement of the canister into the actuator housing towards the support block. It is useful for an inhaler user to know how many doses remain in his or her inhaler (i.e., how much medication by dosage is in the container of the aerosol dispensing assembly). To this end, a reliable dose counter device and methodology is desired, in order to register how many doses have been dispensed from an aerosol dispensing assembly and in order to inform a user how many more doses still remain to be dispensed.
There have been numerous proposals, such as in WO2005/060535 A2 and WO2004/041334, for dose counters to be used with inhalers (whether the inhaler is, for example, a dry powder inhaler, a portable nebulizer, or a pressurized metered dose inhaler, or some other type). However, despite progress, there is still an important need for dose counters which are both economic and reliable.